Punch die and die design
The punch and die are the core working parts of a punch and die, directly involved in the material shearing and separation process. Their structural design, dimensional accuracy, and material properties have a decisive impact on the quality of the stamped part and the life of the die. The design of the punch and die must be based on factors such as the part’s shape, size, material thickness, and production batch size. The optimal structural form, dimensional parameters, and material selection must be determined to ensure smooth material separation during the stamping process and produce high-quality parts.
The structural design of the punch must consider strength, rigidity, and processability. Common punch structures include integral, stepped, sheathed, and combined types. Integral punches offer simplicity and high strength, making them suitable for simple, small-sized blanking parts. Stepped punches reduce the diameter of the non-working portion, reducing weight and facilitating securement, making them suitable for longer punches. Sheathed punches incorporate a sheath over the working portion, enhancing rigidity and wear resistance, making them suitable for slender punches. Combined punches are constructed from multiple parts for ease of machining and replacement, making them suitable for complex shapes. The working length of the punch should be determined based on the material thickness, stripper plate thickness, and guide gauge thickness. It is generally 2-4 times the material thickness plus the thickness of the stripper plate and guide gauge to ensure adequate guidance and strength. For example, for a 2mm thick sheet, the working length of the punch can be 15-20mm.
The structural design of the die must consider material discharge convenience, strength, and rigidity. Common die structures include integral, block, insert, and tapered dies. Integral dies offer high strength and rigidity, making them suitable for simple, small blanking parts. Block dies are composed of multiple blocks, making them convenient for processing large or complex shapes while saving valuable mold materials. Insert dies incorporate carbide inserts within the die body, improving wear resistance and making them suitable for mass production. The cutting edge of a tapered die has a certain taper to facilitate waste discharge and is suitable for blanking thick sheet metal. Die cutting edges come in two types: flat and beveled. Flat edges are suitable for blanking parts requiring high precision, while beveled edges reduce blanking force and are suitable for thick sheet metal or large blanking parts.
Punches and dies must meet stringent dimensional accuracy and form and position tolerances. The dimensional accuracy of the working parts is generally IT6-IT7, and the perpendicularity error of the cutting edge should not exceed 0.01mm/100mm to ensure uniformity in the blanking gap. The surface roughness of the punch and die must be high, with the working surface roughness controlled within Ra0.8-0.1μm to reduce friction with the material and improve wear resistance. For punches and dies with complex shapes, precision machining methods such as wire cutting and electrical discharge machining are required to ensure dimensional accuracy and surface quality. Furthermore, the cutting edges of the punch and die should be sharp, avoiding rounded corners or burrs, which can cause burrs or tears in the blanked parts.
The material selection for the punch and die depends on the part’s material, thickness, and production batch. Commonly used materials include alloy tool steels such as Cr12, Cr12MoV, and CrWMn, as well as cemented carbide. Cr12MoV offers high hardness and wear resistance, reaching a hardness of HRC58-62 after quenching, making it suitable for blanking dies used in medium-volume production. Cemented carbide, with its high hardness (HRC65-70) and excellent wear resistance, is also brittle, making it suitable for large-scale production or high-speed stamping, such as continuous blanking of electronic components. The heat treatment process for both the punch and die is crucial, ensuring high hardness and wear resistance in the working portion and a certain degree of toughness in the core to prevent chipping or fracture during the stamping process.
The fixing method of the punch and die must ensure a firm connection and accurate positioning. Common fixing methods include press-in, screw fixing and riveting. The press-in fixation uses an interference fit to press the punch or die into the fixed plate, which provides a firm connection and is suitable for small and medium-sized punches and dies. The screw fixation fixes the punch or die to the fixed plate with screws and pins, which is easy to replace and is suitable for large or complex-shaped punches and dies. The riveted fixation fixes the punch or die to the fixed plate by riveting the tail of the punch or die and is suitable for small punches. After fixing, it is necessary to ensure that the working surfaces of the punch and die are perpendicular to the reference plane of the fixed plate, with an error not exceeding 0.02mm/100mm to ensure uniform blanking gap. By rationally designing the structure, size and fixing method of the punch and die, the performance and service life of the blanking die can be significantly improved, and the quality of the blanked parts can be guaranteed.
